Method and apparatus for implantable cardiac lead integrity analysis

ABSTRACT

The present invention relates, generally, to scientific and medical system methods for diagnosis of implantable cardioverter defibrillator (ICD) lead conductor anomalies, in particular conductor migration and externalization within an ICD implantable cardiac lead. The method uses an “imaginary” component of the high frequency transmission line impedance having certain spectral changes that correspond to movements of the conductor or an “imaginary impedance”. This allows the detection of conductor migration and small insulation failures.

RELATED APPLICATION

The present application is a Divisional of U.S. application Ser. No.13/842,838, filed Mar. 15, 2013, now U.S. Pat. No. 9,675,799, issuedJun. 13, 2016, which claims the benefit of U.S. Provisional ApplicationNo. 61/733,713 filed Dec. 5, 2012, which are incorporated herein intheir entirety by reference.

FIELD OF THE INVENTION

The present invention relates generally to electrical therapeuticsystems for applying electrical therapy to patients for detecting and/ortreating cardiac arrhythmias. More particularly, the invention relatesto a method and apparatus for analyzing implantable cardiac leads topromote patient safety by evaluating possible issues with implantablecardiac lead integrity, including partial insulation failures, conductormigration, and/or externalization of conductors in multilumen leads.

BACKGROUND

Implantable cardioverter defibrillators (ICDs) are used to providevarious types of therapy to treat cardiac arrhythmias in a patient,including, for example defibrillation. These devices typically consistof a hermetic housing implanted into a patient and connected to at leastone defibrillation electrode. The housing of the ICD contains electroniccircuitry for monitoring the condition of the patient's heart, usuallythrough sensing electrodes, and also contains the battery, high voltagecircuitry, and control circuitry to generate, control, and deliverdefibrillation shocks. Typically, one or more of the defibrillationelectrodes are connected to circuitry within the ICD via one or moreimplantable cardiac leads that extend from the housing to thedefibrillation electrodes. The housing of the ICD may also include oneor more defibrillation electrodes configured on the exterior of thehousing.

Implantable transvenous ICD leads are generally elongated lead bodiesmade of biocompatible insulation material(s) including multiple parallellumens with each lumen carrying one or more conductors that run betweenconnectors on a proximal end to electrodes proximate a distal portion ofthe implantable cardiac lead. The number of conductors required fortrue-bipolar ICD implantable cardiac leads is typically four (twoconductors for sensing and pacing that provide conduction paths for alower power sensed signal and a ground return, and two conductors fortherapy that provide conduction paths for higher power defibrillationshocks, a therapy signal and a ground return). Integrated-bipolar leadscan combine one defibrillation electrode as a pace-sense electrode andthus have only three conductors. In addition, a separate center innercoil and stylet lumen may be provided for use in implanting the ICDimplantable cardiac lead. The center inner coils may also includeconductors that carry electric signals to pacing sense/therapyelectrodes. The diameter of the implantable cardiac lead body must besmall enough to navigate the blood vessels through which the implantablecardiac lead is implanted, while still being robust enough to maintainelectrical and mechanical integrity over the course of bending andmovement during hundreds of thousands of heart beats and respirations.

The long-term reliability and safety of implantable cardiac leads is asignificant issue. Conductor anomalies in the implantable cardiac leadsfor ICDs can result in morbidity and/or mortality from loss of pacing,inappropriate ICD shocks, and/or ineffective treatment of ventriculartachycardia or ventricular fibrillation. The early diagnosis ofconductor anomalies for implantable cardiac leads is a criticallyimportant step in reducing these issues and making ICDs safer.

One particular conductor anomaly that is unique to implantable cardiacleads occurs when a conductor migrates through the soft siliconematerial of the implantable cardiac lead body away from the originalposition of the conductor within a lumen. This problem was originallydescribed for St. Jude's recalled Riata™ and Riata ST™ leads, and theyare considered as illustrative examples. In some cases, the cableincluding the conductor may abrade against the lumen that constrains itto migrate outwardly within the silicone implantable cardiac lead body(“inside-out” abrasion) without breaking through the external insulatinglayer of the implantable cardiac lead body. In other cases, theconductor may continue to abrade against the silicone elastomer leadbody until it breaks through the surface and become externalized andexposed to body fluids and tissue. At this stage, it may be detected byfluoroscopy. Initially, the thin polymer (ETFE) insulating layersurrounding the cable remains intact, at least without delivery ofhigh-voltage shocks. Over time, this ETFE secondary insulating layer can(rarely) become abraded or damaged due one of various mechanisms.Exposed conductors can also result in sensing of nonphysiologicalelectrical signals, “noise”, if the exposed conductor is connected to asensing electrode. This results in incorrect detection of ventriculartachycardia or fibrillation (over-sensing) that may result inunnecessary painful shocks. Even more worrisome, this problem may resultin failed defibrillation shocks if the conductor is connected to theprimary (distal) shock coil located in the right ventricle (RV). In thiscase, the patient will likely die of the arrhythmia unless promptlydefibrillated by an external defibrillator. Failed defibrillation shocksare particularly likely if the conductor to the RV shock coil abradesagainst the proximal shock coil in the superior vena cava (SVC)resulting in a short circuit when a shock is needed. Such“under-the-coil” abrasions may occur without exteriorized cables so thatthey are undetectable by fluoroscopy, hence only detected when a shockis delivered. It is not known how often or the extent to whichearly-stage failures of outer insulation may compromise sensing and/ordefibrillation.

Further, exteriorized cables are not helpful in identifying inside-outabrasions occurring in Riata ST Optim™ and similar Durata Leads™. Theseleads are designed similarly to the Riata and Riata ST have anadditional, abrasion-resistant coating of silicone-polyurethanecopolymer (Optim™) tubing on the external surface. Intact, externaltubing prevents cables that have abraded through their lumens fromexteriorizing, but it does not alter the fundamental process of“inside-out” abrasion. Under the shock-coils, coated leads are identicalto similarly-designed leads without tubing, and they provide noadditional protection against inside-out, cable-coil abrasion.Presently, there is no way to detect inside-out abrasions in coatedleads unless an electrical abnormality resulting in lead failure occurs.

Numerous approaches have been suggested for trying to diagnosis andcorrect for the problems of implantable cardiac lead failures andanomalies. Most involve the classic approach of subjecting theimplantable cardiac lead to a periodic test pulse, measuring thedirect-current impedance of the test pulse, and then comparing thatimpedance to an expected range of acceptable impedance values. Inimplantable cardiac leads, however, only one end of the conductor isgenerally accessible for testing purposes and changes in systemimpedance may be dominated by changes unrelated to conductor orimplantable cardiac lead faults. For example, the reference impedancefor pace-sense conductors is in the range of about 15-50Ω, and usuallyis constant within about 10% for an individual conductor. But thereference impedance for the combined electrode-tissue interface andconnected body tissue ranges from about 300Ω to greater than 1000Ω. Moreimportantly, biological variations of up to 300Ω are common, andvariations of greater than 1000Ω may occur without conductor orinsulation failures. The impact of these normal impedance variations ontraditional impedance-based implantable cardiac lead integrity testingis only now being understood as discussed, for example, in a paper byone of the inventors (Swerdlow, JACC, 2011).

Other potential solutions to address these problem in the sensing anddetection process of the implantable device have been suggested inpapers by one of the inventors, either by increasing the number ofinterval counts (NIC) used by the detection algorithm (Swerdlow,Circulation, 2008), or by using a sensing integrity counter (SIC) tomonitor high numbers of possible over-sensing events (Gunderson, HeartRhythm Society, 2010). The results of testing an improved implantablecardiac lead integrity algorithm (LIA) based on a combination ofabnormally high impedance and over-sensing of non-sustained tachycardiasare reported in (Swerdlow, Circulation 2010). Published patentapplications and patents by the inventors have described otherapproaches for addressing these problems, e.g., US2011/0054554;US2011/0054558; US2010/0228307; US2009/0099615; U.S. Pat. No. 7,747,320;and U.S. Pat. No. 8,200,330.

Unfortunately, none of these approaches provide a good solution for theunique problems of diagnosis and analysis of conductor anomalies due tomigration and/or externalization. At present, there is no testingavailable to determine if the conductors are migrating in theimplantable cardiac lead body as there is no “ohmic” short or parasiticpathway. Even when the conductors have become externalized andpotentially abraded, it is not possible to detect this insulationfailure as the small parasitic conduction through the insulation breakis swamped by minor variations in the higher resistance of the measuredcurrent path including one or more defibrillation electrode coils or thepace-sense electrodes. And, over-estimating the potential forimplantable cardiac lead conductor anomalies has its own negativeconsequences, as a false positive may result in an unnecessaryimplantable cardiac lead replacement surgery, with corresponding expenseand risk.

What is desired are method and apparatus that could analyze and identifyimplantable cardiac lead conductor anomalies at the subclinical stage,before they present as a clinical problem, and do so with a highsensitivity and specificity that minimizes false positives forimplantable cardiac lead conductor anomalies.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide methods and apparatus foranalyzing implantable cardiac leads to promote patient safety byevaluating possible issues with implantable cardiac lead integrity,including conductor migration and/or externalization. Instead of aclassic impedance-based integrity test, an “imaginary” component of ahigh frequency transmission line impedance test having certain spectralchanges, that correspond to movements of the conductor in relation tothe outer insulation, is utilized to diagnose potential implantablecardiac lead integrity issues. This “imaginary impedance” test allowsfor the detection and identification of conductor migration and smallinsulation failures in implantable cardiac leads.

In one embodiment, a method of detecting conductor migration and/orexternalization within an implantable cardiac lead includes the steps ofdetermining an implantable cardiac lead length, calculating a testfrequency based on the implantable cardiac lead length, applying afrequency signal source to the implantable cardiac lead, wherein thefrequencies are within 10% of the test frequency, measuring an imaginarycomponent of a transmission line impedance of the implantable cardiaclead, and determining whether the imaginary impedance increasedapproximately 90% or greater at the test frequency. If so, the methodcan further include additional evaluation and indication of a detectionof a potential conductor migration and/or small insulation failures inan implantable cardiac lead.

In another embodiment, a method of detecting conductor migration and/orexternalization within an implantable cardiac lead includes applying ahigh-frequency signal source to an implantable cardiac lead, the signalsource providing frequencies of 100 MHz or higher to the implantablecardiac lead, measuring an imaginary component of a transmission lineimpedance of the implantable cardiac lead, and determining whether theimaginary impedance increased at frequencies in the range of 170 MHz to190 MHz. A further aspect of this embodiment can include determining ahighest frequency of imaginary impedance increase and estimating alocation of externalization by calculating a one-quarter wavelength fromthe implantable cardiac lead end. Again, this method can further includeadditional evaluation and indication of a detection of a potentialconductor migration and/or small insulation failures in an implantablecardiac lead.

In another embodiment, a method of detecting conductor migration and/orexternalization within an implantable cardiac lead comprises applying afrequency signal source to an implantable cardiac lead, the signalsource providing frequencies of 100 MHz or higher to the implantablecardiac lead, measuring an imaginary component of a transmission lineimpedance of the implantable cardiac lead during a frequency sweep of100 MHz to 200 MHz, and determining a decrease in the peak imaginaryimpedance to 217Ω or less. Again, this method can further includeadditional evaluation and indication of a detection of a potentialconductor migration and/or small insulation failures in an implantablecardiac lead.

In another embodiment, a method of detecting conductor migration,damage, insulation abrasion or externalization within an implantablecardiac lead having an implantable cardiac lead length of less than 2 mimplanted proximate and in electrical communication with a heart of apatient comprises using a source to apply a test signal to theimplantable cardiac lead, wherein the test signal has a signal frequencygreater than 10 MHz, measuring an imaginary component of a transmissionline impedance of the implantable cardiac lead in response to the testsignal, comparing the imaginary component of the transmission lineimpedance to an expected value of the imaginary component of thetransmission line impedance at the signal frequency, and providing anindication of potential lead failure related to conductor migration,damage, insulation abrasion or externalization within the implantablecardiac lead based on whether the imaginary component of thetransmission line impedance is increased relative to the expected value.

According to additional aspects of this embodiment, using the sourcecomprises determining an approximate propagation speed in theimplantable cardiac lead, calculating a test frequency based on thepropagation speed and the implantable cardiac lead length, and causingthe source to apply the test signal is applied at signal frequencieswithin 10% of the test frequency. According to another aspect of thisembodiment, the indication of potential lead failure occurs when theimaginary component of the transmission line impedance is increased byat least 90% to the expected value at the test frequency. According tostill other aspects of this embodiment, the signal frequency is between100 MHz and 200 MHz. According to further aspects of this embodiment,the signal frequency is between 150 MHz and 175 MHz. According toadditional aspects of this embodiment, using the source to apply thetest signal is performed to cause the test signal to sweep acrossmultiple signal frequencies in a frequency sweep band, and wherein theimaginary component of the transmission line impedance is comparedrelative to the expected value over the frequency sweep band. Accordingto additional aspects of this embodiment, the frequency sweep band isbetween 150 MHz and 175 MHz. According to additional aspects of thisembodiment, the source is provided within an implantable cardiac device,and the method performed by the implantable cardiac device. According toembodiments, the source is obtained from a crystal frequency oscillatorthat is also utilized for radio frequency communications by theimplantable cardiac device. This method can further include additionalevaluation and indication of a detection of a potential conductormigration and/or small insulation failures in an implantable cardiaclead. Embodiments can therefore provide such evaluation and indicationutilizing the electronic circuitry of the ICD, and not, for example, anexternal frequency oscillator.

In another embodiment, an apparatus for detecting conductor migrationand/or externalization within an implantable cardiac lead comprises animplantable lead tester housed within the ICD. A microcontroller withanalog I/O controls the implantable lead tester. The circuitry for theimplantable lead tester can include the microcontroller feeding at leastone voltage-controlled oscillator which in turn feeds at least one inputof a high-frequency multiplier thus providing a squaring function. Thesignal is then fed to a DC blocking capacitor resulting in a doubling ofthe frequency. This frequency, as a “carrier” signal is fed into aQuadrature Demodulator (QD). A sense resistor is provided a current (asa voltage drop) that is fed from the resistor to the QD as the RFsignal. Outputs of the QD are then fed back to the microcontroller asI_(REAL) and I_(IM). The sensed current is isolated, rectified, andsmoothed with a diode, resistor and capacitor and fed back to themicrocontroller as I_(RECT) as is the VCO voltage with a separate diode,resistor and capacitor and fed back as V_(RECT). Using the inputs, themicrocontroller can then calculate the real and imaginary impedances.

In another embodiment, the ICD circuitry comprises an energy storagecapacitor and an H-bridge. The H-bridge can be provided with a number ofswitches. The output of this configuration drives the RV coil cable. Afeed-thru capacitor is provided to block RF interference. A MOSFET isprovided between the feed-thru capacitor and ground with the lead testerinserted between the output of the feed-thru capacitor and the gate ofthe MOSFET. In one embodiment the ICD circuitry can be included as partof the ICD while in other embodiments, it can be external to the ICD.

Systems for automatically, semi-automatically or manually initiating thevarious embodiments of the present invention can be provided as part ofcircuitry and/or software within an implantable device, as part of adiagnostic device, or any combination thereof.

Another significant advantage of various embodiments of the presentinvention is the ability to accurately measure impedance withoutaffecting the heart without risk of any cardiac effect due to the veryhigh frequency nature of the test signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 depicts an ICD pulse generator connected to a patient's heart viaa transvenous implantable cardiac lead used for pacing anddefibrillation, the implantable cardiac lead having an externalizedconductor within a chamber of the heart.

FIG. 2 is a cross-sectional view of a multi-lumen ICD implantablecardiac lead.

FIG. 3 illustrates the change in transmission line impedance as theconductor migrates towards the outer limits of the implantable cardiaclead body.

FIG. 4 illustrates the imaginary impedance spectrum for a normalimplantable cardiac lead in a saline solution.

FIG. 5 illustrates the imaginary impedance for an ICD implantablecardiac lead with 1 cm of externalized right ventricular cable.

FIG. 6 illustrates the ratio of imaginary impedance for an implantablecardiac lead with externalized cable versus a normal cable.

FIG. 7 illustrates the statistical confidence of discrimination.

FIG. 8 illustrates the statistical confidence of discrimination for100-200 MHz.

FIG. 9 illustrates the spectrum of utility of measurement.

FIG. 10 illustrates the utility of measurement for 120-180 MHz.

FIG. 11 illustrates the imaginary impedance with an exposed conductor.

FIG. 12 illustrates the ration of imaginary impedance for an implantablecardiac lead with an exposed conductor in a normal cable.

FIG. 13 illustrates the statistical confidence of discrimination.

FIG. 14 illustrates the spectrum of measurement utility for an imaginaryimpedance ration for an exposed conductor.

FIG. 15 illustrates the ratio of imaginary impedance for an implantablecardiac lead with an exposed conductor versus an externalized cable.

FIG. 16 illustrates an embodiment of stand-alone implantable lead testercircuitry for high-frequency implantable lead testing.

FIG. 17 illustrates an embodiment of an implantable lead tester disposedwithin an ICD.

FIG. 18 depicts the connection jig to give repeatable impedanceconnections as used in testing conductors.

FIG. 19 depicts the method of externalizing the conductor with the useof a toothpick for testing.

FIG. 20 illustrates a table that details the lead name, lead serialnumber, model number, and the distance from tip where theexternalization was introduced on the RV coil conductor during testing.

FIG. 21 illustrates the test results of changes in Z_(real) withexternalization on the RV coil conductor.

FIG. 22 illustrates the test results of changes in Z_(real) withexternalization from 140 MHz to 210 MHz on the RV coil conductor.

FIG. 23 illustrates the test results of changes in Z_(imag) withexternalization on the RV coil conductor.

FIG. 24 illustrates the test results of changes in Z_(imag) withexternalization from 150 MHz to 200 MHz on the RV coil conductor.

FIG. 25 illustrates lead 10 in normal condition during testing on the RVcoil conductor.

FIG. 26 illustrates lead 10 after externalization of the RV coilconductor during testing.

FIG. 27 illustrates lead 11 after externalization of the RV coilconductor during testing.

FIG. 28 illustrates lead 12 after externalization of the RV coilconductor during testing.

FIG. 29 illustrates lead 13 after externalization of the RV coilconductor during testing.

FIG. 30 illustrates lead 14 after externalization of the RV coilconductor during testing.

FIG. 31 illustrates the test results of changes in Z_(real) withexposure on the RV coil conductor.

FIG. 32 illustrates the test results of changes in Z_(real) withexposure from 0 MHz to 250 MHz on the RV coil conductor.

FIG. 33 illustrates the test results of changes in Z_(imag) withexposure on the RV coil conductor.

FIG. 34 illustrates the test results of changes in Z_(imag) withexposure from 20 MHz to 220 MHz on the RV coil conductor.

FIG. 35 illustrates the impedance spectrum difference between exposedand externalized on the RV coil conductors during testing.

FIG. 36 illustrates the impedance spectrum difference between exposedand externalized RV coil conductors from 0 MHz to 220 MHz duringtesting.

FIG. 37 illustrates the impedance shift with RV coil conductor exposurefor Lead 10 during testing.

FIG. 38 illustrates the impedance shift with RV coil conductor exposurefor Lead 11 during testing.

FIG. 39 illustrates the impedance shift with RV coil conductor exposurefor Lead 12 during testing.

FIG. 40 illustrates the impedance shift with RV coil conductor exposurefor Lead 13 during testing.

FIG. 41 illustrates the impedance shift with RV coil conductor exposurefor Lead 14 during testing.

FIG. 42 illustrates the testing results for swept frequencies from 100MHz to 200 MHz for the RV coil conductor Z_(imag) for an exposedconductor.

FIG. 43 illustrates a table that details the lead name, lead serialnumber, model number, and the distance from tip where theexternalization was introduced on the ring conductor during testing.

FIG. 44 illustrates the changes in Z_(real) with externalization of aring conductor during testing.

FIG. 45 illustrates the changes in Z_(real) with externalization of aring conductor from 10 MHz to 100 MHz during testing.

FIG. 46 illustrates the Z_(real) high frequency impedance from 850 MHzto 950 MHz on an externalized ring conductor during testing.

FIG. 47 illustrates the changes in Z_(imag) with externalization of aring conductor during testing.

FIG. 48 illustrates the changes in Z_(imag) with externalization of aring conductor from 10 MHz to 100 MHz during testing.

FIG. 49 illustrates the changes in Z_(imag) with externalization of aring conductor from 400 MHz to 500 MHz during testing.

FIG. 50 illustrates the testing results for the real and imaginaryspectra for the 18 cm ring conductor externalization.

FIG. 51 illustrates the testing results for the real and imaginaryspectra for the 18 cm ring conductor externalization from 10 MHz to 100MHz.

FIG. 52A is a block diagram of a system for internally analyzing animplantable cardiac lead within an ICD.

FIG. 52B is a block diagram of a system for externally analyzing animplantable cardiac lead outside of an ICD.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The embodiments of the present invention provide methods and apparatusfor analyzing implantable cardiac leads to promote patient safety byevaluating possible issues with lead integrity, including conductormigration and/or externalization. The embodiments use an “imaginary”component of a high frequency transmission line impedance test havingcertain spectral changes that correspond to movements of the conductorto diagnose potential implantable cardiac lead integrity issues. This“imaginary impedance” test allows for the detection and identificationof conductor migration and small insulation failures in implantablecardiac leads.

One application applies to diagnosis of conductor anomalies inimplantable cardiac leads attached to an implantable medical device witha pulse generator, such as an ICD. Referring to FIG. 1, the implantablecardiac lead system 10 includes an implantable cardioverterdefibrillator (ICD) pulse generator 12 and an implantable cardiac lead14. The implantable cardiac lead 14 comprises an elongated lead body 16enclosing conductors 22. In this application, the ICD 12 is implanted inthe chest of a human patient, and the implantable cardiac lead 14extends to the heart 20. The implantable cardiac lead 14 may beimplanted intra-cardiac as shown, but may alternatively be deployedintravascularly or subcutaneously. Long term reliability and safety ofimplantable cardiac leads 14 is an issue and one particular conductor 22anomaly, as is depicted in FIG. 1, occurs when a conductor 22 migratesto the limits of the implantable cardiac lead body 16, breaks throughthe implantable cardiac lead outer insulation, and becomes externalized.In some instances, the insulation covering the externalized conductor 22can abrade thus exposing the conductor 22 to body fluids and tissue.

A cross-sectional view of a multi-lumen ICD implantable cardiac leadknown to have a propensity for migration and/or externalization failuresis illustrated in FIG. 2. The implantable cardiac lead 14 is comprisedof a lumen and center inner coil 30 surrounded by PTFE insulation 32, aplurality of lumens 34 each containing a pair of conductors 22 with eachconductor 22 surrounded by ETFE insulation 38, an outer insulating layer40, and a silicone insulation 42 disposed between the inner coil PTFEinsulation 32 and the outer insulating layer 40. The plurality of lumens34 are disposed in the silicone insulation 42. The conductors 22 carryelectric current to the anode pace/sense electrode, high voltage RVcoil, and high voltage SVC coil. The conductors 22 are known to migratethrough the soft silicone insulation 42 and can break through the outerinsulating layer 40 thus becoming externalized. While this cardiac lead14 is described as an example of an implanted lead that may experiencevarious lead failure or degradation issues, it will be recognized thatthe various embodiments of the present invention are not limited to thisparticular type of lead and may be applied more generally to a varietyof implantable leads for cardiac nerve or tissue sensing and/orstimulation.

Disclosed is a method and apparatus for analyzing implantable cardiacleads to promote patient safety by allowing a practitioner to determine,inter alia, if a conductor 22 has migrated within the implantablecardiac lead 14, if the conductor 22 has breached the outer insulatinglayer 40 and become externalized, and if the conductor insulation 38 hasbeen abraded or damaged. The method uses an “imaginary” component of thehigh frequency transmission line impedance having certain spectralchanges that correspond to movements of the conductor 22, hereinafterreferred to as “imaginary impedance”. This “imaginary impedance” allowsthe detection of conductor 22 migration and small insulation 38failures.

Referring to FIG. 2, depicting a cross-sectional view of a knownmulti-lumen implantable cardiac lead 14, the outer diameter D of theimplantable cardiac lead 14 is about 2.08 mm. The conductor 22 diameterd is about 0.21 mm and including its ETFE insulation 38, the insulatedconductor 22 diameter d1 is about 0.27 mm. The conductor 22 offset δ,which is the center of the implantable cardiac lead 14 to the center ofthe conductor 22, is about 0.64 mm.

It is known that the transmission line impedance (TLZ) of a coaxialcable is given by the standard formula:Z _(o)=60 log_(e)(D/d)/√{square root over (k)}  (equation 1)where D is the outer diameter, d is the conductor diameter and κ is therelative permeability of the insulator compared to a vacuum. Therelative permeability is about 3 for silicone and about 2.5 for ETFE.Thus, for a silicone implantable cardiac lead with the dimensionalcharacteristics of the known implantable cardiac lead 14, assuming thatthe conductor 22 was centered within the implantable cardiac lead 14,the transmission line impedance simplifies to:Z _(o)=34.6 log_(e)(D/d)  (equation 2)Thus, for a silicone implantable cardiac lead 14 of diameter 2.08 mm anda conductor 22 diameter of 0.21 mm, the TLZ is approximately 80Ω.

However, this result requires that the conductor 22 be in the center ofthe implantable cardiac lead 14, similarly to a coaxial cable, and thisis not the case in the implantable cardiac lead 14 of FIG. 2.Calculation of TLZ for an implantable cardiac lead having an offsetconductor 22 requires formulas of more complexity. A geometricalcorrection factor x is given by:

$\begin{matrix}{x = \frac{d^{2} + D^{2} - {4\;\delta^{2}}}{2\;{dD}}} & \left( {{equation}\mspace{14mu} 3} \right)\end{matrix}$where δ is the delta or offset of the conductor 22 from the center ofthe implantable cardiac lead 14 body. The TLZ is then given by:Z _(o)=34.6[x+√(x ²−1)]  (equation 4)Therefore, since the implantable cardiac lead 14 has a δ of 0.64 mm, theTLZ for the implantable cardiac lead 14 of FIG. 2 would be 62.6Ω, whichis less than the TLZ of the centered conductor. The thin layer of ETFE38 would very slightly increase the TLZ because the permittivity of ETFEis about 2.5, but this effect is negligible and can be ignored. Inaddition, a small error is introduced because the outer “conductor” ofthe transmission line is not metal but blood, which is essentiallysaline at high frequencies. This small error can also be ignored.

As the conductor 22 migrates towards the exterior of the implantablecardiac lead 14 body, but before the conductor 22 externalizes, amaximum offset δ can be determined by the following equation where thethickness, 0.27 mm, of the ETFE 38 is included since at this point, thelayer of ETFE 38 will be outside of the implantable cardiac lead 14body:D/2−d/2=0.906 mm  (equation 5)And, as is illustrated in FIG. 3, the TLZ drops significantly as theconductor 22 migrates towards the outer limits of the implantablecardiac lead 14 through the silicone body 42.

A fully externalized conductor 22 will provide the ultimate limit of theTLZ:Z _(o)=10Ω=60 log_(e)(D/d)/√{square root over (k)}  (equation 6)Where κ=2.5 for ETFE and d=0.27 mm.

Based on these calculations, it is evident that there is a stronglyaffected physical parameter that would vary with the migration of aninternal conductor 22 within a silicone implantable cardiac lead 24body, even without externalization of the cable or breach of the innerETFE insulation. It would vary more with externalization of theconductor 22.

In experimentation, a conductor 22 within an implantable cardiac lead 14was chosen whose migration would be difficult to detect usingconventional lead failure techniques. The conductor 22, in this case, isthe RV coil with a low frequency impedance of about 60Ω as measured bystandard techniques. A saltwater aquarium having a salinity to give abulk resistivity of 100 Ωcm, thus mimicking the resistivity of blood athigh frequencies, was used to contain the implantable cardiac lead 14. Anetwork analyzer was used to measure the real and imaginary impedancefor various frequencies.

To begin, the approximate propagation speed V in an implantable cardiaclead, without anomalies, was determined using the following equation:V=c/√{square root over (k)}  (equation 7)where c is the speed of light in a vacuum (30 cm/ns). For siliconeinsulation 42 this results in an approximate propagation velocity of17.3 cm/ns. This is approximate because the ICD implantable cardiac lead14 is more complex than a classic coaxial cable having a centralconductor.

For an ICD implantable cardiac lead 14 having a common length of 65 cm,the “round-trip” travel distance for wave propagation is 130 cm. Thefrequency is determined by:f=V/λ  (equation 8)where λ is the wavelength of the test frequency. Thus, with apropagation velocity of 17.3 cm/ns, a null at about 130 MHz would beexpected as this corresponds to a ½ wavelength over the full length ofthe implantable cardiac lead 14.

Testing was performed on a normal conductor 22, known to be withoutmigration or defects, for frequencies from 10-200 MHz. Each testedfrequency was tested two times and the results averaged. As depicted inFIG. 4, detailing an imaginary impedance (Z_(im)) spectrum for a normalimplantable cardiac lead in saline, a null occurred at 130 MHz thusconfirming approximate behavior as a transmission line. Additionally,the peak imaginary impedance (Z_(im)) decreased from 235Ω to 200Ωconfirming that externalization can be detected with dependence on acritical frequency.

Testing was then performed on an implantable cardiac lead 14 in which ananomaly was introduced. Due to the difficulty of modeling an internalmigration of the conductor 22 within the implantable cardiac lead 14, an˜1 cm defect was introduced near the RV coil, distant from theimplantable cardiac lead attachment pins, resulting in a slightexternalization of the conductor 22 without conductor 22 exposure (withETFE 38 intact). The conductor 22 was externalized to ˜1 mm from theimplantable cardiac lead 14 body. As can be seen in FIG. 5, a spectrumfor an implantable cardiac lead 14 with 1 cm of externalized RVconductor 22, the high frequency imaginary impedance (Z_(im)) wassignificantly reduced compared to the implantable cardiac lead 14without anomalies.

Ratios of the imaginary impedances were then calculated with theresultant spectrum depicted in FIG. 6. Thus, FIG. 6 depicts the ratio ofimaginary impedances for an implantable cardiac lead 14 with anexternalized conductor 22 versus an implantable cardiac lead 14 withoutanomalies. The ratio illustrates a strong peak from about 120 MHz to 133MHz. And, all of the frequencies about ˜140 MHz had a reduced imaginaryimpedance (Z_(im)). Thus, using the testing methods as detailed above, aslight externalization was able to be detected.

As part of the testing process, simple clip conductors were connected tothe implantable lead connector pins to give a worse-case test ofrepeatability since slight variations in implantable cardiac leadconnections can influence the transmission line impedance (TLZ).

Further analysis and proofing of the testing method was then performed.For example, for each of the externalized conductor 22 and non-anomalyconductor 22 readings, the difference was calculated at each frequencygiving stability values of:S(f)=abs(Z _(im1) −Z _(im2))  (equation 9)The statistical confidence was then calculated using the formula:

$\begin{matrix}{{Confidence} = \frac{{abs}\left( {{Z_{im}{normal}} - {Z_{im}{externalized}}} \right)}{{S{normal}} + {S{externalized}}}} & \left( {{equation}\mspace{14mu} 10} \right)\end{matrix}$resulting in FIG. 7, a statistical confidence of discrimination. A19-point moving average of the confidence values was used to reducespurious values and arrive at the statistical significance. As can beseen in FIG. 7, there is a minimal statistical confidence in the readingdifferences below 100 MHz so these are not shown in FIG. 8 (astatistical confidence of discrimination for 100-200 MHz). Asillustrated, a value greater than 2 shows high confidence in thediscrimination power. The technique as described has high statisticalsignificance for frequencies of 123-127 MHz, 147-154 MHz, and 166-189MHz.

A valued clinical measurement has both “clinical” significance (i.e. thevalue changes greatly) but also “statistical” significance (i.e. thechanges are not due to noise). Thus, a “utility” value can be calculatedat each frequency with the formula given as:Utility=% change×statistical confidence  (equation 11)

A “utility” value of 200 corresponds to a 100% change with a statisticalconfidence of 2.0. This combination is unusually strong for any type ofclinical diagnosis. The utility values are depicted in FIGS. 9 and 10,with FIG. 10 showing the utility of measurement for the 120 MHz to 180MHz spectrum only. In this embodiment, the present invention hasrecognized that a shift in the imaginary impedance at the frequencies123-128 MHz, 146-153 MHz, and 168-176 MHz gives a powerful diagnostic ofa conductor 22 externalization. The peak at 125 MHz corresponds to theimplantable cardiac lead length and the externalization was introducedat 50 cm from the beginning of the implantable cardiac lead 14(connection pins). For the 50 cm distance to the externalization, thefull-wavelength critical frequency is given by:f=V/λ  (equation 12)where λ is the wavelength of the test frequency. Thus, with apropagation velocity of 17.3 cm/ns, a null at about 172 MHz would beexpected as this corresponds to a one-quarter wavelength over thisdistance. And, while there is no simple explanation for the middle peakat 150 MHz, it is clearly demonstrated as a result of theexperimentation.

Further experimentation was performed using the imaginary impedancecomponent to detect conductor 22 exposure (ETFE 38 not intact). Theconductor 22 was exposed by removing approximately 2-3 mm of ETFE 38insulation. Testing was performed, similarly as detailed above for aconductor with no anomalies and an externalized conductor, and FIG. 11depicts that the imaginary impedance at high frequencies was able todetect conductor exposure.

As can be seen in FIGS. 12 and 13, the changes in imaginary impedanceare even greater for an exposed conductor than for one that isexternalized. FIG. 12 illustrates the ratio of Z_(im) for an implantablecardiac lead with exposed conductors and the impedance increase has apronounced peak at 131 MHz. FIG. 13 depicts the statistical confidenceof discrimination with a peak at 120 MHz.

FIG. 14 further depicts the spectrum of measurement utility for animaginary impedance ratio for the exposed conductor 22. This illustratesstrong diagnostic capability of this method from 119-139 MHz with a peakat 130 MHz.

In another embodiment, the imaginary impedance component can be used todifferentially detect conductor exposure versus conductorexternalization. An advantage to determining the type of anomaly is thata determination can be made as to the urgency of replacing theimplantable cardiac lead 14. FIG. 15 depicts the ratio of Z_(im) for animplantable cardiac lead with an exposed conductor versus anexternalized conductor.

The examples in the above methods assume that the test signals would begenerated from within the implantable pulse generator via specialtesting apparatus 50, as depicted in FIG. 16, stand-alone lead testercircuitry 50 for high-frequency lead testing. Microcontroller (μC) withanalog I/O 52 controls the system 50. Microcontroller (μC) 52 sweepsthru frequencies of interest by delivering appropriate voltages to atleast 1 voltage-controlled oscillator (VCO) 54. As an example, the VCO54 could be the Crystek CVCO33CL-0110-0150 which sweeps the range130-150 MHz thus capturing the 1^(st) peak as shown in FIG. 7. Aplurality of VCOs 54 can be configured to capture additional peaks andthe outputs can be summed via resistors 56.

This outputted signal:V(t)=sin(2πft)  (equation 13)is then fed to the input of the high-frequency (500 MHz) multiplier 58,an example being the Analog Devices AD834. The multiplier provides asquaring function resulting in an output voltage of:sin²(2πft)=½−½ cos(4πft)  (equation 14)which is fed through DC blocking capacitor converting the signal to:½ sin(4πft)  (equation 15)by removing the ½ offset and phase shifting the −cos into a sinfunction. Note that the frequency is now doubled. The doubled frequencysignal is fed into a Quadrature Demodulator 62 as the “carrier” signal.An example of a Quadrature Demodulator 62 is the Linear TechnologyLT5517 which can perform up to 900 MHz.

The sense resistor R_(s) senses the current (as a voltage drop). Thevoltage drop is fed to the Quadrature Demodulator 62 as the RF signal.An impedance matching LC network is provided prior to the RF inputs ofthe Quadrature Demodulator 62 but the details are omitted in the figurefor clarity. The Quadrature Demodulator 62 outputs the real andimaginary components of the current (I_(REAL) and I_(IM) respectively)which are then fed to the μC 52.

The sensed current signal is amplifier 66 isolated, rectified, andsmoothed with the diode 68, resistor 70 and capacitor 72. The DC signalis then fed back to the μC 52 as I_(RECT). The VCO voltage is alsorectified and smoothed with the diode 74, resistor 76, and capacitor 78.The DC signal is then fed back to the μC 52 as V_(RECT).

The vector value of the impedance is calculated by the μC 52 as:Z _(abs) =V _(RECT) /I _(RECT)  (equation 16)

The μC 52 further calculates the real and imaginary components of theimpedance from I_(REAL) and I_(IM).

FIG. 17 is an embodiment of an implantable lead tester 50 housed withinan ICD 80. An energy storage capacitor 82 provides energy to theH-bridge shown with the 4 switches 84. The output of the H-bridge drivesthe RV coil cable. In conventional ICDs, this signal passes thru afeed-thru capacitor having a typical value of 1 nF designed to block RFinterference, for example, a mobile phone in a shirt pocket.Unfortunately, at the frequencies of interest, the feed-thru capacitorrepresents a shunt of about 1Ω to ground thus precluding impedancespectrum measurements:Z=1/(2πf)=1.13Ω at 140 MHz  (equation 17)

In order to perform implantable lead testing as disclosed and to preventthe shunting operation, an embodiment of the implantable lead testeruses a high voltage MOSFET 86 to connect the 1 nF capacitor 88 to theICD can. The impedance measuring circuit 50 is provided in parallel tothe output of the capacitor 88 and the gate of the MOSFET 86. Duringimpedance spectral testing, MOSFET 86 is open and the impedance testingsignal is fed thru the impedance measuring circuit 50 (a standard MOSFETcontrol circuit is not shown for clarity). During normal operation theMOSFET is ON, the signal bypasses the impedance measuring circuit 50,and the capacitor 88 serves to shunt interference. In addition, theMOSFET 86 protects the impedance measuring circuitry 50 fromdefibrillation shocks. Similar circuitry is used for the lower-voltagepacing and sensing connections.

In an alternative embodiment, the impedance spectral testing signal isfed thru the non-capacitive feed-thru that is used by the RFcommunications antenna. A magnetic reed switch or MOSFET is then used toconnect this “antenna” signal to the appropriate cable in the ICD lead.

Testing Results

As discussed above, in experimentation, conductors 22 within animplantable cardiac lead 14 were chosen whose migration would bedifficult to detect. One conductor 22 is the RV coil with a lowfrequency impedance of about 60Ω as measured by standard techniques. Thesecond conductor 22 is the ring conductor. A saltwater aquarium 100having a salinity to give a bulk resistivity of 100 Ωcm, thus mimickingthe resistivity of blood at high frequencies, was used to contain theimplantable cardiac lead 14. As shown in FIG. 18, a custom builtconnection jig 102 was used to give repeatable impedance connections. Anetwork analyzer was used to measure the real and imaginary impedancefor various frequencies.

Testing was performed on externalized RV coil conductors 22,externalized ring conductors 22, and exposed RV coil conductors 22.Tested were five Riata® 65.0 cm leads 14 for each of the test scenarios.For each lead 14, the conductors 22 were either externalized or exposedat 9.0 cm from tip (n=2) and 18 cm from tip (n=3). Externalization wasto the precise thickness of a standard wooden toothpick 104 as shown inFIG. 19. For externalization of the RV coil conductors 22 and theexternalized ring conductors 22, the real and imaginary impedance wastested from 10 MHz to 1000 MHz with the lead in saline at 100 Ωcmresistivity.

First, the RV coil conductors 22 were externalized. FIG. 20 is a tablethat details the lead name, lead serial number, model number, and thedistance from tip where the externalization was introduced.

The beginning for the RV coil is 58.5 cm from the lead 14 connection.Assuming a dielectric constant of 3.0 for the silicone this would give ahalf-wave frequency of ˜150 MHz. Indeed, the Z_(real) peaked atapproximately 500Ω while Z_(Imag) was about 0 at 150 MHz thus confirmingreasonable transmission line behavior. The Z_(mean) shift was calculatedfor all five leads 14. Also the number of standard deviations (NSD) ofshift was calculated for each lead 14 at each frequency. The standarddeviation was determined from the five leads 14 before modifications.

As seen in FIG. 21, there were two strong peaks with 6- and 8-sigmashifts. These shifts each had percent shifts of >>10% which was thethreshold set for accuracy confidence. As seen in FIG. 22, these peaksare quite robust. The peak at 195 MHz has a confidence of >4 sigma fromapproximately 186 MHz to approximately 204 MHz.

As seen in FIG. 23, there is a single strong peak in the Z_(imag)response. This single strong peak is seen zoomed in FIG. 24 and has apeak of 18 sigma at approximately 170 MHz. It has statistical confidenceof >4 sigma from 164 MHz to 175 MHz. Shown in FIG. 25 is a normalimpedance spectrum for Lead 10. This normal impedance spectrum issimilar to the normal impedance spectrum for Leads 11 to 14. Thespectral shifts in FIG. 25 are shown for about 100 MHz to about 250 MHzas these have the frequencies where the shifts are statisticallysignificant. FIGS. 26 to 30 are individual lead impedance spectralshifts with externalization for Leads 10 to 14. With the conductorexternalized there is an increase in Z_(imag) at about 170 MHz and adrop in Z_(real) at about 195 MHz.

Thus, based on testing results, it can be concluded that externalizationcan be detected with a high degree of confidence by noting changes inthe Z_(real) at 195 MHz and Z_(imag) at 170 MHz.

Second, testing was performed for the detection of an exposed RV coilconductor 22. An ETFE ribbon having a length of approximately 5 mm wasscraped off the conductor 22 at the site of the externalization and theimpedance spectrum measurements were repeated.

As seen in FIG. 31, there are a number of Z_(real) significant peaksextending out to 950 MHz. However, the lower frequency peaks are themost dramatic so the focus was trained on those. In particular, focuswas on the usable peaks at 50 MHz, 155 MHz, and 200 MHz, which are shownzoomed in FIG. 32. Changes in Z_(imag) were measured and as seen in FIG.33, Z_(imag) has many usable spectral peaks. There is an intriguing peakat approximately 775 MHz but it just reaches 4 sigma. However, in FIG.34 (which is a portion of FIG. 33 zoomed), Z_(imag) has a very broadpeak at approximately 170 MHz that is >4 sigma from approximately 162MHz to approximately 215 MHz. That breadth suggests a very robust andrepeatable measurement parameter. There is also a usable peak for thisembodiment at about 56 MHz.

Thus, based on testing results, it can be concluded that conductor 22exposure can be detected with a high degree of confidence by notingchanges in the Z_(real) at approximately 200 MHz and Z_(imag) atapproximately 170 MHz.

As shown in FIG. 35 and FIG. 36, the testing process further resulted innoting a subtle difference between exposed RV coil conductors 22 andexternalized intact conductors 22. The largest difference appears to beat the lower frequency limit of 10 MHz which suggests that a lower RFfrequency might be used. There are fairly broad peaks at 30 and 120 MHz,in Z_(imag), of about 2 sigma. Thus, it is possible to differentiate,with the disclosed technique, between an exposed and merely externalizedRV coil conductor 22.

FIGS. 37 to 41 are individual lead impedance spectral shifts withexposure for Leads 10 to 14 where a separate testing was done byperforming a simple test of sweeping to find the minimum Z_(imag). Thespectral shifts are shown for 100 MHz to 300 MHz as these have thefrequencies where the shifts are statistically significant. With theconductor 22 exposed there is an increase in Z_(imag) at about 160 MHzand a drop in Z_(real) at about 145 MHz.

FIG. 42 highlights the results where rather than focusing on a specificfrequency, the frequencies from 100 MHz to 200 MHz were swept and theminimum value for Z_(imag) was noted. Z_(imag) runs negative for most ofthis band so the less negative value is sought. If that is lessnegative, i.e., >−290Ω, then a faulty RV coil conductor 22 can bediagnosed. Note that the Z_(imag) increase is substantial with a rangeof 4.46 to 11.90 standard deviations.

Thus, based on these results, it can be concluded that conductor 22exposure can be detected with a high degree of confidence by performinga simple test of sweeping to find the minimum Z_(imag).

Third, the ring conductors 22 were externalized. FIG. 43 is a table thatdetails the lead name, lead serial number, model number, and thedistance from tip where the externalization was introduced.

The Z_(mean) shift was calculated for all 5 leads. Also the number ofstandard deviations (NSD) of shift was calculated for each lead at eachfrequency. The standard deviation was determined from the 5 leads beforemodifications. As seen in FIG. 44, there were 2 peaks with 4 and 3-sigmashifts. These peaks each had shifts of 8% and 3%, which were not high.

As seen in FIG. 45, the peak at 65 MHz is not robust having a 4-sigmashift. It is also fairly narrow thus raising the possibility that itcould be noise from multiple comparisons. There is a subtle “peak” at910 MHz (see FIG. 46) of 3 sigma. However, since it is fairly wide (>2sigma from 890-935 MHz) it can represent a true shift.

As seen in FIG. 47, there are 2 peaks in the Z_(imag) response at about50 MHz and about 450 MHz. While each are only about 3 sigma theyrepresent large value shifts (>>10%) and as such, represent genuinechanges. The first low frequency peak is seen zoomed in FIG. 48 and hasa peak of 3.2 sigma at about 56 MHz. The second low frequency peak isseen zoomed in FIG. 49 and has a peak of 3.2 sigma at 440 MHz with avery large value shift.

It is concluded that externalization of the ring conductor 22 can bedetected by noting changes in the Z_(real) at about 65 MHz and about 910MHz and Z_(imag) at about 56 MHz and about 440 MHz. The differences aremore subtle than those seen with externalization of the RV coilconductor 22.

Another analysis was performed on leads 10, 12, and 14 which had theexternalization at 18 cm from the tip. This additional analysis wasperformed to determine if the subtle changes involved with ringconductor 22 externalization were affected by the consolidation of the 9cm and 18 cm location data. FIG. 50 illustrates the real and imaginaryspectra for just the 18 cm ring conductor externalization. As seen inFIG. 51, this analysis at 18 cm produced a stronger and wider peak inthe real impedance at about 21 MHz. Note that the earlier peak at 65 MHzis still here almost unchanged. That may be a marker for a ringconductor 22 externalization anywhere.

However, the strong and wide peak at 21 MHz may be unique to anexternalization location near 18 cm from the tip. Recall that thesampling was done with logarithmic frequency iterations. Thus, there areas many samples from 10-100 MHz as there are from 100-1000 MHz.

The peak at 21 MHz has about 500 samples where the shift is ≥2 sigma.That is 10% of the overall 5000 samples. Thus, a ring conductor 22externalization, at 18 cm, can be detected.

In embodiments, the imaginary impedance test allows for the detectionand identification of conductor migration and small insulation failuresin implantable cardiac leads, where the test for imaginary impedance canutilize components to generate a high frequency test signal internal to,for example, ICD 12. In other embodiments, methods of detectingconductor migration, damage, insulation abrasion, or externalizationwithin an implantable cardiac lead can be generated from a highfrequency test signal source external to ICD 12.

Referring to FIG. 52A, an implantable cardiac lead system can utilize anICD pulse generator 200, for example, having a crystal frequencyoscillator 202 used in methods of internally detecting conductormigration, damage, insulation abrasion or externalization within animplantable cardiac lead. In some embodiments, the crystal frequencyoscillator 202 is also utilized for radio frequency communications 204by the implantable cardiac device 12. In embodiments, the crystalfrequency oscillator 202 can be used to generate a high frequency testsignal(s) for use in accordance with various embodiments as described.In one embodiment, a single target high frequency signal is used toconduct a rough evaluation of the imaginary impedance. For example, inan embodiment and referring to FIG. 52A, ICD 12 can include within ICDbody 206, a microprocessor 210, a high-frequency signal source component212, an oscillator 202, a radio frequency component 216 operably coupledto a radio antenna 218, and a high voltage therapy capacitor system 220.The high voltage therapy capacitor system 220 is conventional and iscoupled to lead connectors 230 in ICD header 208 by a high frequencycapacitor filter/isolation arrangement. In this embodiment, a frequencydivider 214 is operably coupled between the oscillator 202 and thehigh-frequency signal component 212 that is controlled by themicroprocessor 210. In this embodiment, the oscillator 202 is configuredto provide the frequency for RF communications, for examples, using theMICS band between 401 and 406 MHz, and the frequency divider isconfigured with flipflops, for example, to divide this frequency down toa frequency between 100-200 MHz that may be utilized in accordance withthe various embodiments. A high-frequency test pulse can be commandedalong the cardiac lead by the microprocessor 210 through thehigh-frequency component 212, and a switch arrangement 224.

If the rough evaluation of the imaginary impedance in response to thehigh frequency test signal generated internally within the ICD 200indicates a deviation from an expected value, further testing andevaluation can be indicated to be performed, for example, by an externalsystem such as shown in FIG. 52B. If the rough evaluation indicates adeviation, the lead system can be connected by an adapter cable 250 to ahigh frequency signal source generator 252 that is external to the ICD12. In embodiments, the pre-indication analyzed from the source signalswithin the ICD 12 can be further analyzed by any of the various sweepfrequency band methods utilizing pulse generators external to, forexample, ICD 12. For example, the cardiac lead can be operably coupledwith an adapter cable to an external pulse generator after a rough,pre-indication of imaginary impedance from the source signals within theICD 12 is greater than expected.

For example, in an embodiment and referring to FIG. 52B, the externalhigh frequency pulse generator may comprises a laptop or other computingdevice, an external signal source, and an adapter cable. The adaptercable can be configured to operably couple to the cardiac lead in orderto provide signals, as described in the myriad methods above, along thecardiac lead. In embodiments, the laptop is operably coupled to andconfigured to control the external signal source. In other embodiments,the external signal source can provide its own signal outputconfiguration.

The values noted above are example embodiments and should not be read aslimiting the scope of this invention. Those skilled in the art willrecognize that the above values may be adjusted to practice theinvention as necessary depending on the electrode implantable cardiaclead technology used and the physical characteristics of the patient.

While the present invention has been described with reference to certainembodiments, those skilled in the art should appreciate that they canreadily use the disclosed conception and specific embodiments as a basisfor designing or modifying other structures for carrying out the samepurposes of the present invention without departing from the spirit andscope of the invention as defined by the appended claims.

The following patents and applications, the disclosures of which areincorporated by reference in this case (other than claims and expressdefinitions), are prior art attempts by common inventors to solve theproblem at issue: U.S. Pat. No. 8,352,033 ('033) to Kroll, issued Jan.8, 2013; U.S. patent application Ser. No. 13/735,599 to Kroll, filed onJan. 7, 2013 which is a continuation of '033; and U.S. patentapplication Ser. No. 12/868,056 to Swerdlow, filed on Aug. 25, 2010.

The following provisional applications, the disclosures of which areincorporated by reference in this case (other than claims and expressdefinitions), are related to each other: U.S. Patent Application61/689,191 to Kroll and Swerdlow, filed on Jun. 1, 2012; U.S. PatentApplication 61/689,189 to Kroll and Swerdlow, filed on Jun. 1, 2012; andU.S. Patent Application 61/733,713 to Kroll and Swerdlow, filed on Dec.5, 2012.

The invention claimed is:
 1. A system for analyzing an implantablecardiac lead implanted proximate and in electrical communication with aheart of a patient, the system comprising: an implantable cardiac leadincluding one or more high-voltage conductors, each high voltageconductor being electrically connected to at least one defibrillationelectrode; and an implantable cardioverter defibrillator (ICD) device inelectrical communication with the implantable cardiac lead including: aradio adapted to transmit and receive RF transmissions related to theoperation of the implantable cardiac device, a high frequency testcircuit adapted to generate a high frequency test signal greater than 10MHz for application to the implantable cardiac lead; a frequencyoscillator configured to provide a frequency for the RF transmissionsand for the high frequency test circuit; and, a microcontrollerconfigured to control the radio and the high frequency test circuitry togenerate a high frequency test signal that is applied to at least one ofthe one or more high-voltage conductors of the implantable cardiac lead,determine an imaginary component of a transmission line impedance of theimplantable cardiac lead in response to the test signal, and communicatevia the radio an indication of potential lead failure related toconductor migration, damage, insulation abrasion or externalizationwithin the implantable cardiac lead based on whether the imaginarycomponent of the transmission line impedance is increased relative to aexpected value.
 2. The system of claim 1, further comprising: anexternal high frequency pulse generator; and an adapter cable operablycoupleable to the implantable cardiac lead, wherein the external highfrequency pulse generator is operably adapted to generate a multitude ofhigh frequency pulses to be applied to the implantable cardiac lead overa frequency sweep range to confirm whether the indication of a potentiallead failure is correct.